PLATELET AUTOANTIBODIES (IGG, IGM, IGA) AGAINST GLYCOPROTEINS IIB IIIA AND IB/IX IN PATIENTS WITH THROMBOCYTOPENIA/

Autoimmune thrombocytopenic purpura (AITP) is most frequently induced by platelet-specific autoantibodies against epitopes on platelet GP Ib /IX or GP IIb/IIIa. These antibodies are reliably detected on the pati ents' autologous platelets, So far, studies on the characterization of platelet autoantibodies have been restricted to IgG antibodies. We us ed the monoclonal antibody immobilization of platelet antigens assay ( MAIPA) in a modified version to detect GP-specific IgG, IgM, and IgA a ntibodies. Platelets of 46.2% of patients carried elevated amounts of IgG antibodies. IgM and IgA antibodies were observed less frequently a nd showed only weak OD signals in the MAIPA assay. Circulating IgG ant ibodies in serum were found in 11.5% of patients. Circulating IgM auto antibodies were observed in 8.9% and IgA antibodies in no patient with AITP. Results of direct MAIPB assay were compared with the reactivity of eluates in the platelet adhesion immunofluorescence assay and were found to be highly concordant. Patients with AITP in remission carrie d high percentages of anti-GP IIb/IIIa. Findings made in this study su ggest that autoantibodies of the IgM and IgA classes play only a minor role in the pathogenesis of AITP.